1. Field of the Invention
The invention relates to an apparatus of maximum likelihood signal detection, and more particularly to an apparatus that realizes maximum likelihood detection for detecting signals with different characteristics. The apparatus of maximum likelihood signal detection can be used to detect signals with different channel responses, coding constraints and channel memory lengths.
2. Description of Related Art
A conventional apparatus of maximum likelihood signal detection makes use of the Viterbit algorithm for signal detection or decoding, and is thus also called a Viterbit decoder or a Viterbit detector. The conventional Viterbit algorithm is usually used in communication systems or data storage systems, and can be used for decoding of convolutional codes, detection of baseband signals of wireless communication systems or detection of data recorded on a harddisk.
With gradual popularity of optical discs in recent years, the demand of increasing the capacity of optical discs rises more and more. In order to increase the data capacity of optical discs, many specifications of optical discs have been worked out, e.g., VCD, DVD, HDDVD and Blue-ray disc. However, because optical discs generally record data with lands and pits, in order to meet the demand of increasing capacities of optical discs, the formed lands and pits will be denser. Hence it makes reading of the data from the optical disk becoming more difficult. Therefore, in orders to conquer the problem of data reading, manufacturers utilize partial response maximum likelihood (PRML) devices with the Viterbit decoder for data detection.
FIG. 1 is a block diagram of a conventional Viterbit decoder applied in a partial response maximum likelihood device. As shown in FIG. 1, a Viterbit decoder 10 comprises a branch metric unit 101, an add-compare-select unit 103, a path metric unit 105, a path memory 107 and a reference information unit 109.
The branch metric unit 101 is used for receiving reference information outputted by the reference information unit 109 and a sampled data signal to calculate out a first calculation value and also for outputting the first calculation value to the add-compare-select unit 103. The reference information is a reference signal level of a branch. The first calculation value is a branch metric of the branch. The add-compare-select unit 103 performs addition, comparison and selection actions to generate a second calculation value (i.e., a survival path metric), and transmits the survival path metric to the path metric unit 105 to update the path metric stored in the path metric unit 105.
The add-compare-select unit 103 will retrieve the latest path metric from the path metric unit 105 to perform addition, comparison and selection actions so as to generate the next second calculation value. Besides, the add-compare-select unit 103 will also transmit its determination result (i.e., a determination bit) to the path memory 107 to temporarily store the survival path into the path memory 107. Next, the path memory 107 will output the path data to a next-stage device for subsequent data processing. Generally, the addition, comparison and selection actions of the add-compare-select unit 103 are carried out in turn. But some methods, however, the addition action and comparison action are performed parallel to enhance the operational speed. Although various embodiments of the invention are exemplified with the add-compare-select unit, the invention also applies to these kinds of methods with faster operational speeds.
Data signals reproduced from various optical discs, however, may have different characteristics, for example, different channel responses, different coding constraints or different channel memory lengths. In the prior art, various maximum likelihood signal detection apparatuses are therefore used for respectively processing the received data signals from those optical discs, hence easily resulting in waste of resources and increase of the manufacturing cost.